We classify cancer into different stages and now researchers are doing something similar with Alzheimer's disease. It could mean a much earlier diagnosis for many.

Sister Barbara Schlatter has been a nun for 50 years.

"II entered the convent in 1963," Sister Barbara told ABC30.

She's helped a lot of people during that time, but two people she couldn't help were her parents. They both passed away with Alzheimer's. Now, Sister Barbara worries about her aging brain.

"When I can't get a word, I think, uh oh, is this it?" Sister Barbara said.

Recently, investigators found a way to "stage" the disease during a period they call "pre-clinical Alzheimer's."

"The data suggests that, the pathology starts anywhere from 10 to 20 years before any sign of clinical symptoms," Anne Fagan, PhD, Research Professor, Washington University in St. Louis, told ABC30.

Researchers divide preclinical Alzheimer's into three stages based on results from spinal fluid and imaging tests.

They studied 311 patients. The preclinical stages are based on biomarkers that indicates how much amyloid plaque and tangle-related proteins are found in the brain and whether or not patients eventually go on to show symptoms of memory decline.

"Once you get dementia, that is actually the end stage," Dr. Fagan said.

Sister Barbara hopes the research will one day save others from the heartache she felt watching her parents fade away.

About 31 percent of the 311 patients studied fell into one of the stages. This percentage matched findings from autopsy studies, suggesting that Alzheimer's starts long before symptoms develop.

Researchers believe patients with preclinical Alzheimer's could be an important target for new therapies. Interestingly, the investigators found individuals with preclinical Alzheimer's were six times more likely to die over the next decade, but they aren't sure why.